to some contaminants. Poor — when the index is between 101 and 150. In this value, some sensitive groups can have health effects. Some people can experience minor symptoms, including people with breathing or heart problems, children and old people. At this stage, there is no significant risk for the general public. Harmful — when the index is between 151 and 200. In this situation everybody can experience negative health effects. Members of sensible groups can present serious issues. This interval activates the phases precontingencia (precontingency) and contingencia fase I (1st contingency phase) of the Programa de Contingencias Ambientales Atmosféricas(PCAA) del Valle de México (Atmospheric Environmental Contingencies Program of Mexico City). Extremely Harmful — when the index is more than 201. In this condition the general population may experience very serious symptoms and health effects. Concentration of pollutants during the last decade PM10: According to the NOM, the annual limit for PM10 was 50 μg/m3 before 2014 and 40 μg/m3 from 2015 to present day. In Mexico City, the annual concentration of PM10 has been above the limit for the last 10 years .The highest concentration occurred in November 2019, when the PM10 levels were found to be over 110 μg/m3. Failure to comply with this NOM indicates that it is necessary to carry out actions to reduce the concentration of particulate material in the ambient air, given that it is not observed that there is a tendency to decrease in the concentrations registered for this pollutant criterion in recent years. PM2.5: The values have exceeded the regulated limits (15 μg / m3 before and during 2014 and 12 μg / m3 as of 2015 ) since 2011. In May 2019, the level of PM2.5 reached levels between 150 and 160 μg / m3. This concentrations were reached due to burning of organic matter such as forest fires, firewood, fuel burning, especially diesel and some industrial processes. This concentrations amounts to the equivalent of Mexico City's inhabitants (of all ages) smoking nearly three-and-a-half cigarettes those days. Ozone (O3): The limits for Ozone according to the NOM were 0.11 Parts Per Million before 2014 and 0.095 ppm from 2015 to present times. Over the past two decades, ozone levels gradually fell below government limits as authorities moved factories out of the capital and tightened regulations on fuel and cars. In 2015, 37% of the total days showed poor air quality due